Conformational Restriction and Enantioseparation Increase Potency and Selectivity of Cyanoguanidine-Type Histamine H4 Receptor Agonists

J Med Chem. 2016 Apr 14;59(7):3452-70. doi: 10.1021/acs.jmedchem.6b00120. Epub 2016 Apr 5.

Abstract

2-Cyano-1-[4-(1H-imidazol-4-yl)butyl]-3-[2-(phenylsulfanyl)ethyl]guanidine (UR-PI376, 1) is a potent and selective agonist of the human histamine H4 receptor (hH4R). To gain information on the active conformation, we synthesized analogues of 1 with a cyclopentane-1,3-diyl linker. Affinities and functional activities were determined at recombinant hHxR (x: 1-4) subtypes on Sf9 cell membranes (radioligand binding, [(35)S]GTPγS, or GTPase assays) and in part in luciferase assays on human or mouse H4R (HEK-293 cells). The most potent H4R agonists among 14 racemates were separated by chiral HPLC, yielding eight enantiomerically pure compounds. Configurations were assigned based on X-ray structures of intermediates and a stereocontrolled synthetic pathway. (+)-2-Cyano-1-{[trans-(1S,3S)-3-(1H-imidazol-4-yl)cyclopentyl]methyl}-3-[2-(phenylsulfanyl)ethyl]guanidine ((1S,3S)-UR-RG98, 39a) was the most potent H4R agonist in this series (EC50 11 nM; H4R vs H3R, >100-fold selectivity; H1R, H2R, negligible activities), whereas the optical antipode proved to be an H4R antagonist ([(35)S]GTPγS assay). MD simulations confirmed differential stabilization of the active and inactive H4R state by the enantiomers.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Guanidines / chemistry*
  • Guanidines / pharmacology*
  • Guanosine 5'-O-(3-Thiotriphosphate) / metabolism
  • HEK293 Cells
  • Histamine Agonists / chemistry
  • Histamine Agonists / pharmacology*
  • Humans
  • Imidazoles / chemistry*
  • Imidazoles / pharmacology*
  • Mice
  • Models, Molecular
  • Molecular Conformation
  • Molecular Dynamics Simulation
  • Protein Conformation
  • Radioligand Assay
  • Receptors, G-Protein-Coupled / agonists*
  • Receptors, G-Protein-Coupled / chemistry*
  • Receptors, G-Protein-Coupled / metabolism
  • Receptors, Histamine / chemistry*
  • Receptors, Histamine / metabolism
  • Receptors, Histamine H4
  • Sf9 Cells
  • Spodoptera
  • Stereoisomerism
  • Structure-Activity Relationship

Substances

  • 2-cyano-1-(4-(1H-imidazol-4-yl)butyl)-3-((2-phenylthio)ethyl)guanidine
  • Guanidines
  • HRH4 protein, human
  • Histamine Agonists
  • Imidazoles
  • Receptors, G-Protein-Coupled
  • Receptors, Histamine
  • Receptors, Histamine H4
  • UR-RG98
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • dicyandiamido